Resolve clippy::useless_conversion

    error: useless conversion to the same type: `rustc_const_eval::interpret::Pointer<std::option::Option<machine::Tag>>`
       --> src/helpers.rs:668:36
        |
    668 |                 this.get_ptr_alloc(ptr.offset(len, this)?.into(), size1, Align::ONE)?.unwrap(); // not a ZST, so we will get a result
        |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider removing `.into()`: `ptr.offset(len, this)?`
        |
        = note: `-D clippy::useless-conversion` implied by `-D clippy::all`
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_conversion

    error: useless conversion to the same type: `rustc_const_eval::interpret::Pointer<std::option::Option<machine::Tag>>`
       --> src/helpers.rs:678:29
        |
    678 |         this.read_bytes_ptr(ptr.into(), len)
        |                             ^^^^^^^^^^ help: consider removing `.into()`: `ptr`
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_conversion

    error: useless conversion to the same type: `rustc_const_eval::interpret::Pointer<std::option::Option<machine::Tag>>`
       --> src/helpers.rs:690:44
        |
    690 |             let alloc = this.get_ptr_alloc(ptr.into(), size2, align2)?.unwrap(); // not a ZST, so we will get a result
        |                                            ^^^^^^^^^^ help: consider removing `.into()`: `ptr`
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_conversion

    error: useless conversion to the same type: `rustc_const_eval::interpret::OpTy<machine::Tag>`
       --> src/shims/intrinsics.rs:778:42
        |
    778 |                         .read_immediate(&this.operand_index(index, i)?.into())?
        |                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider removing `.into()`: `this.operand_index(index, i)?`
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_conversion

    error: useless conversion to the same type: `u32`
        --> src/shims/posix/fs.rs:1171:26
         |
    1171 |             builder.mode(mode.into());
         |                          ^^^^^^^^^^^ help: consider removing `.into()`: `mode`
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_conversion

    error: useless conversion to the same type: `std::ffi::OsString`
      --> src/shims/env.rs:67:53
       |
    67 |                     ecx.machine.env_vars.map.insert(OsString::from(name), var_ptr);
       |                                                     ^^^^^^^^^^^^^^^^^^^^ help: consider removing `OsString::from()`: `name`
       |
       = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_conversion

    error: useless conversion to the same type: `rustc_const_eval::interpret::Scalar<machine::Tag>`
       --> src/shims/tls.rs:102:44
        |
    102 |                 Ok(value.unwrap_or_else(|| Scalar::null_ptr(cx).into()))
        |                                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider removing `.into()`: `Scalar::null_ptr(cx)`
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_conversion

    error: useless conversion to the same type: `u32`
      --> src/thread.rs:73:26
       |
    73 |         Scalar::from_u32(u32::try_from(self.0).unwrap())
       |                          ^^^^^^^^^^^^^^^^^^^^^
       |
       = help: consider removing `u32::try_from()`
       = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_conversion

Author: dtolnay

src/helpers.rs

@@ -664,8 +664,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         loop {
             // FIXME: We are re-getting the allocation each time around the loop.
             // Would be nice if we could somehow "extend" an existing AllocRange.
-            let alloc =
-                this.get_ptr_alloc(ptr.offset(len, this)?.into(), size1, Align::ONE)?.unwrap(); // not a ZST, so we will get a result
+            let alloc = this.get_ptr_alloc(ptr.offset(len, this)?, size1, Align::ONE)?.unwrap(); // not a ZST, so we will get a result
             let byte = alloc.read_scalar(alloc_range(Size::ZERO, size1))?.to_u8()?;
             if byte == 0 {
                 break;
@@ -675,7 +674,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         }
 
         // Step 2: get the bytes.
-        this.read_bytes_ptr(ptr.into(), len)
+        this.read_bytes_ptr(ptr, len)
     }
 
     fn read_wide_str(&self, mut ptr: Pointer<Option<Tag>>) -> InterpResult<'tcx, Vec<u16>> {
@@ -687,7 +686,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         loop {
             // FIXME: We are re-getting the allocation each time around the loop.
             // Would be nice if we could somehow "extend" an existing AllocRange.
-            let alloc = this.get_ptr_alloc(ptr.into(), size2, align2)?.unwrap(); // not a ZST, so we will get a result
+            let alloc = this.get_ptr_alloc(ptr, size2, align2)?.unwrap(); // not a ZST, so we will get a result
             let wchar = alloc.read_scalar(alloc_range(Size::ZERO, size2))?.to_u16()?;
             if wchar == 0 {
                 break;

src/lib.rs

@@ -21,7 +21,6 @@
     clippy::needless_lifetimes,
     clippy::new_without_default,
     clippy::single_match,
-    clippy::useless_conversion,
     clippy::useless_format
 )]
 

src/shims/env.rs

@@ -64,7 +64,7 @@ impl<'tcx> EnvVars<'tcx> {
                                 unsupported
                             ),
                     };
-                    ecx.machine.env_vars.map.insert(OsString::from(name), var_ptr);
+                    ecx.machine.env_vars.map.insert(name, var_ptr);
                 }
             }
         }

src/shims/intrinsics.rs

@@ -775,7 +775,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
 
                 for i in 0..dest_len {
                     let src_index: u64 = this
-                        .read_immediate(&this.operand_index(index, i)?.into())?
+                        .read_immediate(&this.operand_index(index, i)?)?
                         .to_scalar()?
                         .to_u32()?
                         .into();

src/shims/posix/fs.rs

@@ -1168,7 +1168,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         #[cfg(unix)]
         {
             use std::os::unix::fs::DirBuilderExt;
-            builder.mode(mode.into());
+            builder.mode(mode);
         }
 
         let result = builder.create(path).map(|_| 0i32);

src/shims/tls.rs

@@ -99,7 +99,7 @@ impl<'tcx> TlsData<'tcx> {
             Some(TlsEntry { data, .. }) => {
                 let value = data.get(&thread_id).copied();
                 trace!("TLS key {} for thread {:?} loaded: {:?}", key, thread_id, value);
-                Ok(value.unwrap_or_else(|| Scalar::null_ptr(cx).into()))
+                Ok(value.unwrap_or_else(|| Scalar::null_ptr(cx)))
             }
             None => throw_ub_format!("loading from a non-existing TLS key: {}", key),
         }

src/thread.rs

@@ -70,7 +70,7 @@ impl From<u32> for ThreadId {
 
 impl ThreadId {
     pub fn to_u32_scalar(&self) -> Scalar<Tag> {
-        Scalar::from_u32(u32::try_from(self.0).unwrap())
+        Scalar::from_u32(self.0)
     }
 }